The present invention relates to an elastic shaft coupling which, as a transmission element, has at least one torsion element with an elastically deformable elastomer body to which axial flange connections are attached in a fixed manner on the sides upon which force is applied and removed.
The transmission elements are subjected to substantial dynamical stress under the load changes typically occurring during operation. Such dynamical stress is reflected on the one hand by the considerable elongation stress of the connection between the connection flanges and the elastomer body. On the other hand, viscoelastic effects, i.e. inner friction of the elastomer materials, lead to conversion of mechanical energy into heat. This may lead to the occurrence of local thermal peaks, so called heat clusters because of the relatively low thermal conductivity of the rubber material. Material-specific limit temperatures should basically not be exceeded in this connection because that may otherwise lead to local damage. This applies to a special degree to the zone of the outer jacket surfaces because the expansion reached the highest values in said zone. The result thereof is particularly high load acting on the transition between the rubber-and-metal joint, which, of course, is noteworthy also because of the notch effect occurring on the outer limit edge. Furthermore, heating occurring on the surface of the material, which is accompanied by a mechanical load, should not exceed preset limit values because aging processes occurring there would otherwise be accelerated.
The problems explained above have been successfully counteracted in the prior art through constructional developments, so that rubber couplings are viewed since a fairly long time as entirely reliable construction elements with advantageous operating properties. Through particularly constructive developments, local loads are reduced in that connection to a harmless measure. For this purpose, the occurrence of local mechanical or thermal loads is either limited directly, and/or provision is made for effective cooling. A few measures that are advantageous in this regard are specified, for example in DE 37 10 390 C2, where the connection flanges are provided with the shape of the shell of a cone, so that the rubber body is provided with a V-shaped cross section that widens linearly outwards. Owing to the fact that the axial width of the elastomer body increases radially viewed from the inside to the outside, the outer fibers have a greater elastic length. The lower local expansion resulting therefrom is advantageous in view of the development of heat and the load to which the rubber-metal interfaces are subjected.
The collected lost heat is effectively dissipated via other measures such as a segmented design of the transmission elements, as well as by providing for through-extending cooling windows.
However, the trend to increasingly higher power densities, combined at the same time with a smaller installation space requires a more far-reaching optimization of the elastomer couplings known in the prior art.
An elastic shaft coupling is known from U.S. Pat. No. 2,742,769 which has an elastomer body between two connection flanges. However, it has been found that such elastomer bodies quickly fail in the presence of varying torques mainly on the outer radius even though the torque to be withstood stationarily is not reached.
An elastic shaft coupling with elastomer bodies of the type used in smaller mechanical drives is introduced also in U.S. Pat. No. 2,295,316. However, the shape of the elastomer bodies between the ends of the shaft leads to the fact that the elastomer body is destroyed by local overloads especially at the elastomer-metal interface.
For solving said problem the invention proposes that the axial width of the elastomer body be increased viewed radially from the inside to the outside more than proportionally at least by sections whereby the axial connection flanges (2) have chalice- or bell-shaped shapes in a continuously sweeping form relative to each other without a bend in the elastomer-metal interface.
According to the invention, the cross section of the elastomer body has at least an inner and one outer radial zone, whereby the radial width grows sooner in the outer than in the inner zone as the radius increases. While the width of the elastomer body in the prior art increases only linearly over the entire cross section because of the cone shell-shaped connection flanges, and therefore proportionally, the effective elastic width increases more rapidly to the outside according to the invention, at least by sections.
According to a particularly advantageous embodiment of the invention, provision is made that the cross section of the elastomer body is widened in the form of a bell viewed radially from the inside to the outside. The bell-shaped design, which could be called also chalice- or tulip-shaped, means there is a continuously curved, rounded transition between the individual zones. Avoiding a bent expanse of the connection flanges leads to a uniform load acting on the rubber-metal interface, and unsteadiness is avoided to the greatest possible extent.
The invention, of course, can be realized in the same way both on a through-extending, ring-shaped and a segmented elastomer body.
The special advantage of the invention ensues from the fact that the elastic length in the path in the outer zones is coordinated in a superior way with the mechanical and thermal load occurring there more than proportionally with the radius. Furthermore, the outer jacket surface of the elastomer body is enlarged in this connection to an extent such that lower local elongations issue, and superior dissipation of heat into the ambient air takes place at the same time. The aging effects mentioned above are clearly reduced in this way. The given amount of the overall cross sectional area of the elastomer body results overall in a more homogeneous load. Therefore, the transmittable power density is increased as compared to the designs of couplings known, for example from DE 37 10 390 C2 already cited above, and also DE 33 10 695 C2. This means that the coupling can be designed smaller for a given torque and consequently takes up less installation space. As an alternative it is possible in connection with a coupling with unchanged dimensions to transmit an accordingly high power.
For solving the problems explained above, provision is made according to a particularly advantageous, alternative embodiment that the transmission element has at least one inner elastomer body and at least one outer elastomer body, whereby the elastomer bodies are arranged coaxially with the axis of the coupling and with a radial spacing from each other and have a common connection flange on the driving side and the driven side.
Such an embodiment as defined by the invention can be realized in the same way with couplings according to the prior art cited above, and in conjunction with the elastomer bodies that widen toward the outside more than proportionally as defined by the invention.
As opposed to the prior art, a torsion element designed as defined by the invention has one-piece elastomer bodies not only in the radial direction, but at least two or more ring- or segment-shaped separate elastomer bodies that have a radial spacing from each other, whereby said elastomer bodies each have a radially through-extending, common connection flange both on the driving side and the driven side. This means that the outer elastomer bodies surround the inner elastomer bodies, thereby forming cooling channels that extend through in the peripheral direction.
A special advantage of the invention issues from the fact that the air-flushed cooling channels extending through in the peripheral direction are axially limited by the metallic connection flanges. The heat collected under dynamic load in the poorly thermally conductive rubber material of the elastomer bodies is dissipated in a particularly good way in this manner on account of the fact that air flowing along the cooling channels is directly transferring the heat to the connection flanges, which have good thermal conductivity.
The development of critical local thermal peak loads in the rubber material can be additionally prevented in connection with the invention by providing the highly stressed outer elastomer bodies with smaller radial dimensions. This permits for the first time cooling that is optimally adapted to the local thermal loads, which results in the fact that an advantageous and particularly uniform load is acting on the elastomer material. This ensues the special advantage that both the transmittable power density and the useful life are increased.
With one embodiment of the invention, the elastomer bodies are mounted on common one-piece connection flanges. This means that several inner and outer elastomer bodies are directly attached by vulcanization to a radially through-extending connection flange. The connection flange may be a ring-shaped, single-piece flange, or it may be assembled from ring segments depending on the type of construction of the coupling. When assembled from ring segments, the individual elastomer bodies have the shape of ring segments as well.
According to a particularly advantageous alternative embodiment of the shaft coupling as defined by the invention, provision is made that the inner and outer elastomer bodies are provided with separate connection flange modules for forming transmission element modules, said connection flange modules being successively detachably connectable with each other radially. The special advantage of the present embodiment lies in the fact that shaft couplings can be built in different structural sizes from standardized modules like a modular system. For this purpose, the connection flange modules are peripherally provided with corresponding connection means, for example with drilled flange screw holes. The transmission element modules can be radially cascaded in this way, whereby the common connection flanges each are formed in their totality by the connection flange modules connected with one another.
The module-like structure has the manufacturing advantage that the transmission element modules can be made available stepped with different radii. Shaft couplings for different power classes can then be manufactured with low expenditure without requiring complicated and costly special production series.
A further advantage is that transmission element modules worn in the course of operation can be replaced with low expenditure, and that the fitness of a damaged coupling thus can be restored again within a short time.
The connection flange modules of the transmission element modules are usefully designed in such a way that they can be radially inserted into one another. In such an embodiment, the connection flange modules each project radially beyond the elastomer body. The inner and the outer modules are coordinated with one another in this connection in such a way that the connection flanges of the one module can be plugged radially between the connection flanges of the other module located next to it inwards or outwards. For connecting the connection flange modules with each other in a detachable manner, said modules have corresponding, drilled axial flange holes in the radial marginal zones permiting the modules to be screwed together. The modules are then secured by means of flange bolts.
As an alternative, the transmission element modules may be designed in a segmented form, or through-extending in the form of a ring. With the divided embodiment, the connection flange segments of the outer modules can be readily cascaded radially for mounting them. However, if the connection flange modules are designed in the form of a closed ring, they first have to assembled in the axial direction for their coaxial installation, and then connected with each other in a fixed way by means of suitable connection means, for example by screwing them together. Fastening elements such as, for example flange rings or the like that can be attached later can be employed for said purpose. According to an especially advantageous variation, which can be realized without such additional elements but nonetheless permits a symmetrically interlocked assembly, provision is made that the connection flange modules are designed in a bayonet-type way. In such an embodiment, the connection flanges have corresponding inner and outer bayonets with radial recesses and projections, so that in the mounting position, a flange ring can first be positioned in the axial direction beyond the next-smaller connection flange, and subsequently axially locked in the coaxially installed condition by a relative turn. The projections opposing each other in said locking position are then screwed to each other.
An outer elastomer body is preferably axially wider than an inner elastomer body. This takes into account the fact that the rated shear stress remains constant, viewed radially from the inside to the outside.
In order to achieve a still further enhanced adaptation to the actually occurring loads, it is advantageous that the axial width of the inner and outer elastomer increases more than proportionally at least by sections, viewed from the inside to the outside. The radial elastomer cross section thus is provided with a bell- or tulip-shaped cross section, viewed radially from the inside to the outside. This may relate to both each individual elastomer body and to the totality of the elastomer bodies in the shaft coupling. The local load can be rendered more uniform in this way and the useful life is prolonged accordingly.
Each transmission element may have axially throught-extending cooling windows for improving the cooling efficiency.
Based on the explained drawbacks of the prior art the invention is based on the problem of providing an elastic shaft coupling which, taking into account the material-specific stressability of the elastomer, the low thermal conductivity of elastomers and the outwardly increasing load on the elastomer body, has a low ratio of peak to basic expansion and thus a useful life that is significantly prolonged.
In addition, cooling elements may be embedded in the elastomer body in an undetachable manner. Such cooling elements are structural elements made of material with good thermal conductivity, which extend in the elastomer through core areas with maximum heat development, and outer zones that are cooler in relation to the core zones. Such cooling elements therefore provide for effective heat dissipation from the critical zones. In a torsion element, said cooling elements are preferably realized in the form of axial metal cooling sheets that extent at least up to the outer surface of the respective elastomer body. If such metal cooling sheets project outwards, this has the advantage in terms of manufacturing that that they can be safely and solidly clamped in the protruding zones when the rubber is injected during the vulcanizing operation.
In order to optimize the connection of the elastomer body with the connection flanges also for the highest loads, it is advantageous that the connection flange has axially and/or radially projecting holding shoulders around which the elastomer body extends. Said holding shoulders are preferably provided in the form of ring shoulders with a rounded cross section. Superior adhesion of the vulcanized bond is achieved in this way in the particularly stressed marginal zones.